A cellular communication system projects a number of cells onto the earth. In a terrestrial cellular system, these cells radiate about or from a cell site. Calls placed to subscriber units must be routed through a gateway to a cell site projecting a beam wherein the called subscriber unit resides.
Terrestrial cellular communication systems notify subscriber units of an incoming call by transmitting (paging) a subscriber unit identification number using one or more frequencies within the cell. These paging frequencies are reused in non-adjacent cells.
Subscriber units in terrestrial cellular systems, in contrast to subscriber units in satellite cellular systems, travel at negligible speeds in relation to a cell site. Therefore, Doppler frequencies in terrestrial systems do not significantly spread a paging frequency; however, in a satellite cellular communication system where satellites (cell sites) orbit at speeds of over 20,000 km/hr, Doppler frequency spreading of over 60 kHz to 80 kHz is typical.
Satellite cellular systems implementing multiple frequency reuse of paging frequencies require several broadband (Doppler compensating) paging frequencies consuming significant spectrum.
Additionally, subscriber units in a satellite cellular communication system require control channels (broadcast channels) to provide information pertinent to call termination such as available communication channels. Prior art systems requiring subscriber units to scan multiple channels before control channels are detected consume significant resources and time.
It should be noted, that in a multi-mode communication system where both duplex communication and simplex paging services reside, such as in the case of the present invention, simplex paging retains the paging designation while notification of an incoming call assumes the designation of ring alert.
Thus what is needed is a single ring alert channel to conserve spectrum.
Additionally, what is needed is an easily acquirable and trackable ring alert channel for subscriber units.
Furthermore, what is needed is an efficient method of directing subscriber units to applicable control channels assigned to their present cell.